In recent years it has become common in the semiconductor industry to polish the wafers after successive layers of conductive traces or other structures are formed on their surfaces. This produces very smooth surfaces for repeated photolithographic processes and significantly improves the yield. The polishing process, typically chemical-mechanical polishing (CMP), leaves grit and other debris on the surface of the wafer which must be removed before fabrication process can continue. This has led to the development of wafer cleaning devices, such as the device described in co-pending application Ser. No. 08/663,654, which is incorporated herein by reference in its entirety. Following cleaning, the wafers must be thoroughly dried before they can be returned to the fabrication line.
Wafer spin dryers use a combination of centrifugal force and air flow to remove all moisture from the surface of the wafer. Two known types of spin dryers are illustrated in FIGS. 1 and 2. In the version shown in FIG. 1, a wafer 10 is held by fingers 12 above a platen 13. Platen 13 is rotated on a shaft 14 by a spin motor 15. Rinse water is applied from above by one or more nozzles 16 to the "good" (active) side of wafer 10. A problem with this type of dryer is that the drying chamber 17 is open to the atmosphere, which while normally quite clean still contains particulate matter. Particles which fall onto the wafer during and immediately following the drying operation will remain when the next process step begins.
In the prior art dryer shown in FIG. 2, the drying chamber 20 is not open to the atmosphere from above, and the wafer 10 is held by fingers 21 below the platen 22. The platen is spun by a motor 23 which is mounted above the platen. The good side of the wafer faces downward, and one or more nozzles 24 apply rinse water to wafer 10 from below. A problem with this type of dryer is that water droplets which are thrown from the spinning wafer can strike the surface of the drying chamber and splash against the good side of the wafer.
Thus there is a need for a wafer dryer which avoids the above problems and reliably yields a clean, dry wafer suitable for further processing.